• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.345-345
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• 2006

It is well known that poly(glutamate)s with long n-alkyl side chains form thermotropic liquid crystalline state by melting of the side-chain crystallites and also poly(glutamate)s such as poly(${\gamma}-benzyl\;L-glutamate$ )(PBLG), poly(${\gamma}-n-alkyl\;L-glutamate$), etc. in solvent form the isotropic, biphasic and liquid crystalline phases which contains cholesteric and columnar liquid crystalline forms depending on the polypeptide concentration. Although there is no diffusion study for PBLG in liquid crystalline state, because it is difficult to observed $^{1}H$ spectrum of PBLG in liquid crystalline state for its very short $^{1}H\;T_{2}$. In this study, the diffusional behavior of rodlike PBLG in concentrated solution is successfully elucidated as studied by the field-gradient $^{1}H$ NMR methods.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.8 no.5
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• pp.1215-1219
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• 2007

In this paper, we present a study on the polypropylene/thermotropic liquid crystalline polymer blends. In previous researches, the blends are fabricated at very high temperatures, at least 300oC, since the TLCPs investigated in most studies have melting temperatures higher than 270oC. As a consequence, the thermal degradation of PP can not be avoidable. In order to obtain high physical properties, the excess amount of TLCP must be added. In this study, a new type of TLCP was used in the PP/TLCP blends. Since the new TLCP has a melting point of 220oC, the blending can be performed at much lower temperature than the previous studios. The new PP/TLCP shows similar or somewhat higher physical properties than those of the previous studies. It is proved that the new TLCP can be used as a reinforcement material in PP based blends.

• Macromolecular Research
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• v.11 no.1
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• pp.62-68
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• 2003

Thermotropic liquid crystalline polymer (TLCP)/poly(ethylene 2,6-naphthalate) (PEN)/poly(ethylene terephthalate) (PET) ternary blends were prepared by melt blending, and were melt-spun to fibers at various spinning speeds in an effort to improve fiber performance and processability. Structure and property relationship of TLCP/PEN/PET ternary blend fibers and effects of annealing on those were investigated. The mechanical properties of ternary blend fibers could be significantly improved by annealing, which were attributed to the development of more ordered crystallites and the formation of more perfect crystalline structures. TLCP/PEN/PET ternary blend fibers that annealed at 18$0^{\circ}C$ for 2 h, exhibited the highest values of tensile strength and modulus. The double melting behaviors observed in the annealed ternary blend fibers depended on annealing temperature and time, which might be caused by different lamellae thickness distribution as a result of the melting-reorganization process during the DSC scans.

• Korean Journal of Food Science and Technology
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• v.51 no.5
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• pp.432-437
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• 2019

The objective of this study was to determine the molecular/crystalline structures and phase transition properties of starches isolated from six rice cultivars grown in Korea. Apparent amylose content was highest in starch obtained from the Saemimyeon cultivar (30.8%) and lowest in that obtained from the Sheonhyangheukmi cultivar (20.3%). Starch from the Saemimyeon cultivar had a lower proportion of short chains (DP 6-12) and a the higher proportion of long chains (DP${\geq}37$) than that seen in other rice starches. Saemimyeon had relatively higher pasting temperature ($86.5^{\circ}C$), gelatinization temperature ($72.1^{\circ}C$) and gelatinization enthalpy (14.2 J/g) than these values found for other rice starches. The onset temperature and enthalpy for ice crystallization of rice starch ranged from $-27.1{\sim}-20.2^{\circ}C$ and 241.1~264.8 J/g, respectively. The ice melting enthalpy measured in excess water (67% water content) of rice starches was 282.4~310.1 J/g. Among the rice starches examined, starch obtained from Sheonhyangheukmi, with the lowest amylose content, showed the lowest glass transition temperature (${T_g}^{\prime}$).

• Applied Chemistry for Engineering
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• v.5 no.6
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• pp.1036-1043
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• 1994

The silane crosslinking method was applied for the crosslinking of polyethylene (PE). Crosslinking of PE was performed by, first grafting vinyltrimethoxysilane(VTMOS) to the main chain of PE using an extruder at $200{\sim}210^{\circ}C$, followed by exposure to three different silane crosslinking conditions (1. immersed in $80^{\circ}C$ water, 2. at $80^{\circ}C$ air forced convection oven, 3. exposed to air at room temperature ). The thermal characteristic changes of PE resins with respect to the silane crosslinking conditions were studied by measuring the crystalline melting temperature, density and crosslinking reaction rate. Because silane crosslinking was carried out at solid state, crystalline melting temperature, crystallinity, crystal growth rate, crosslinking reaction rate and the change in the density of silane crosslinked PE were affected by crosslinking condition and the type of base resin. The properties of silane crosslinked PE were different from those of Peroxide crosslinked PE which was crosslinked at the molten state. It was found, from the result of DSC analysis, that silane crosslinked linear low density polyethylene(LLDPE) crosslinked at room temperature had no secondary melting peak because the crosslinking reaction proceeds slowly as the crystalline grows. After crystallization, the melting point of PE was lowered by crystalline interruption of crosslinked site.

• Korean Journal of Materials Research
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• v.19 no.2
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• pp.95-101
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• 2009

Glass ceramics were made from coal bottom ash by adding CaO and $Li_2O$ as glass modifiers and $TiO_2$ as a nucleating agent in a process of melting and quenching followed by a thermal treatment. The surface of the glass ceramics has 1.6 times more $Li_2O$ compared to the inner matrix. When $TiO_2$ was not added or when only 2 wt% was added, the surface parts of the glass ceramics were crystalline with a thickness close to $130{\mu}m$. In addition, the matrixes showed only the glass phase and not the crystalline phase. However, doping of $TiO_2$ from 4 wt% to 10 wt% began to create small crystalline phases in the matrix with an increase in the quantity of the crystalline. The matrix microstructure of glass ceramics containing $TiO_2$ in excess of 8 wt% was a mixture of dark-gray crystalline and white crystalline parts. These two parts had no considerable difference in terms of composition. It was thought that the crystallization mechanism affects the crystal growth, direction and shape and rather than the existence of two types of crystals.

• Fibers and Polymers
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• v.5 no.3
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• pp.245-251
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• 2004

Poly(trimethylene terephthalate-co-trimethylene 2,6-naphthalate)s (P(TT-co-TN)s) with various copolymer composition were synthesized, and their chain structure, thermal property and crystalline structure were investigated by using $^1$H-NMR spectroscopy, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD), respectively. It was found from sequence analysis that all the P(TT-co-TN) copolymers synthesized have a statistical random distribution of TT and TN units. It was also observed from DSC thermograms that the glass transition temperature increases linearly with increasing the TN comonomer content, whereas the melting temperature of copolymer decreases with increasing the corresponding comonomer content in respective PTT- and PTN-based copolymer, showing pseudo-eutectic melting behavior. All the samples melt-crystallized isothermally except for P(TT-co-66 mol % TN) exhibit multiple melting endotherms and clear X-ray diffraction patterns. The multiple melting behavior originates from the dual lamellar population and/or the melting-recrystallization-remelting. The X-ray diffraction patterns are largely divided into two classes depending on the copolymer composition, i.e., PTT and PTN $\beta$-form diffraction patterns, without exhibiting cocrystallization.

• Korea-Australia Rheology Journal
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• v.15 no.3
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• pp.109-115
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• 2003

Rheometry testing and the DSC measurement of five thermotropic liquid crystalline polymers (TLCP) have been carried out. The dynamic viscosities of the five TLCPs show a typical shear-thinning behaviour obeying the power-law with the power indices from 0.2 to 0.3. When these TLCPs are heated above the melting temperatures determined by the DSC measurements, the dynamic viscosities first rapidly decrease by 2～3 orders of magnitude then level off, finally increase gradually with the further increasing of temperature. The steady shearing exhibited the same behaviour as the dynamic shearing, but serious edge fracture of material slippage out of the plates occurred. The abnormal temperature dependence of the viscosities can be explained by the nematic-isotropic transition. By using the concept of activation energy, we propose a simple model which can fit the shear-thinning behaviour quite well and predict qualitatively correct temperature effects.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.7 s.178
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• pp.1703-1711
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• 2000

Microstructural morphology of molded composites of thermotropic liquid crystalline polymer(LCP) and polyamide 6 (PA6) has been studied as a function of epoxy fraction. Injection-moulding of a thin composite plaque at a temperature below the melting point of the LCP fibrils by suing the extruded LCP/PA6 pellets produced multi-layered structures: 1) the surface skin layer with thickness of 65-120 ym exhibiting a transverse orientation, 2) the sub-skin layer with an orientation perpendicular to the surface skin, i.e. in the flow direction, 3) the core layer with arc-curved flow patterns. Similar microstructural orientations were observed in the respective layers for the composite plaques with different fractions of epoxy.

• Fibers and Polymers
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• v.1 no.2
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• pp.83-91
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• 2000

Thermotropic liquid crystalline polymer made up of poly(p-hydroxybenzoate) (PHB)-poly(ethylene terephthalate)(PET) 8/2 copolyester, poly(ethylene 2,6-naphthalate) (PEN) and PET were mechanically blended to pursue the liquid crystalline phase of ternary blends. Complex viscosities of blends decreased with increasing temperature and PHB content. DSC thermal analysis indicated that glass transition temperature (Tg) and melting temperature (Tm) of blends increased with increasing PHB content. Both tensile strength and initial modulus increased with raising PHB content and take-up speed of monofilaments. In the WAXS diagram, only PEN crystal reflection at 2Θ=$15.5^{\circ}C$ appeared but PET crystal reflection was not shown in all compositions. The degree of transesterification and randomness of blends increased with blending time but sequential length of both PEN and PET segment decreased.